Method of clarifying water

ABSTRACT

Water is clarified by flocculation using as a flocculation additive, a dispersion of 1 g./l. of cellulose-free sodium alginate in demineralized water titrating at less than 10* hydrotimetric. The dispersion is added to the water to be treated in an amount corresponding to 0.2-0.5 p.p.m. to alginate.

United States Patent 1 1 3,627,680

[72] Inventor Gilbert Desbos [56] References Cited [2 1 A l N 5 2;:FOREIGN PATENTS 1 pp o.

[22] Filed semis, 1970 487,987 l1/1952 Canada 210/54 451 Patented Dec.14,1971 OTHER REFERENCES [73] Assignee Compagnle des Eaux et de LO neBetz Handbook of Industrial Water Conditioning, Betz Paris, FranceLabs., Inc., 5th Ed., 1957, Phila., Pa., pp. 204, 205 and 208-Continuation of application Ser. No. 804,257, Mar. 4, 1969, nowabandoned. This application Sept. 28, 1970, Ser. No. 76,331

[ 54] METHOD OF CLARIFYING WATER 1 Claim, No Drawings [52] US. Cl210/52,

252/181 [51] Int. Cl C02b 1/20 [50] Field of Search 2lO/42,5l,

Primary Examiner-Michael Rogers Attorney-Waters, Roditi, Schwartz &Nissen ABSTRACT: Water is clarified by flocculation using as aflocculation additive, a dispersion of l g./1. of cellulose-free sodiumalginate in demineralized water titrating at less than 10 hydrotimetric.The dispersion is added to the water to be treated in an amountcorresponding to 0.2-0.5 p.p.m. to alginate.

METHOD OF CLARIFYING WATER This application is a streamlinedcontinuation of application Ser. No. 804,257 filed Mar. 4, I969, nowabandoned.

This invention is concerned with a method of clarifying water, and, moreparticularly, with a method in which impurities are flocculated by meansof a flocculating electrolyte, such as a salt of aluminum, iron or thelike, and the water is clarified by coagulating and deposition of theflue.

It has become standard practice to use the flocculating agent properwith reagents, generally described as flocculation additives," which actas a colloidal charge and are of very varied natures. However, none ofthese additives is really satisfactory. For example, activated silica,which is widely used in the United States and which is obtained byreaction between sodium silicate and sulfuric acid, is subject to thedisadvantage that it necessitates the handling of dangerous chemicalsubstances. In addition the colloidal sol obtained has a certain degreeof instability which can lead to its complete gelification when thematuring time has passed.

The majority of the agents known as polyelectrolytes" are toxic andcannot, therefore, be used in the treatment of drink ing water.

Sodium alginate had also been used for this purpose; it is obtained bythe action of caustic soda on certain species of algae and thecommercial qualities available at present contain variable quantities ofcellulose. In general this alginate is used in a concentration of from 2to 4 p.p.m. in the form of a suspension which is injected into the waterto be treated, the proportion used depending on the nature of the water.

One hundred percent pure sodium alginate, that is completely freed ofcellulose, is commercially available and it might be thought thatlogically it would be more effective than the impure quality. However ithas been found that the use of this pure alginate is totally ineffectivein water treatment. An explanation of this surprising behavior is thatthis alginate, being extremely reactive, forms calcium alginate with thecalcium ions present in the water and thus loses the colloidaldispersion properties for which it is used.

I have now developed a method of using pure sodium alginate as aflocculation additive in water treatment, which method conserves itshigh reactivity and requires the use of a much smaller amount ofalginate, the required concentration of alginate being, in addition,substantially independent of the degree of contamination and thetemperature of the water to be treated.

This method is based on the use of 100 percent pure sodium alginate inthe form of a colloidal dispersion in demineralized water titrating atless than hydrotimetric, the dispersion containing 1 g./l. of thealginate. The term 10 hydrotimetric" is used to define the degree ofhardness of water. It is a conventional term in wide use in France. Onehydrotimetric degree corresponds to 10 p.p.m. hardness expressed asCaCO,. Thus, 10 hydrotimetric is equivalent to 100 p.p.m. of CaCO,. Insuch a dispersion the sodium alginate remains in a very reactive formand can be injected into the water to be treated in an amount of from0.2 to 0.5 p.p.m. to give the same results as are obtained with l0 timesgreater quantities of commercial impure sodium alginate.

According to the present invention, therefore, I provide a method ofclarifying water by flocculation, in which a dispersion of l g./l. ofcellulose-free sodium alginate in demineralized water titrating at lessthan 10 hydrotimetric is used as flocculation additive, the dispersionbeing mixed with the water to be treated to give a concentration of from0.2 to 0.5 p.p.m. of alginate in the water.

In order that the invention may be more fully understood, the followingexamples are given by way of illustration only.

A series of samples of the same contaminated water were treated firstwith the usual amount of a conventional flocculating agent, the amountof the latter being the same for each sample, and then, respectively,with varying amounts of commercially available sodium alginatecontaining 50 percent of cellulose, this material being introduced intothe water to be treated in the form of an aqueous suspension, and with,varymg amounts of a l g./l. dispersion of cellulose-free sodium alginatein demineralized water titrating at less than 10 hydrotimetric. Thecellulose-containing alginate was introduced to give concentrations ofl, 2 and 3 p.p.m. of alginate in the water and the cellulose-freealginate dispersion to give concentrations of 0.3 and 0.5 p.p.m. ofalginate in the water. The coagulation time, in minutes, and theappearance of the flock, characterized in accordance with the Baylisscale, were noted in each case. The results obtained are shown in thefollowing table.

It is apparent from these results that the method according to theinvention enables results comparable to those obtained at present withimpure alginate, to be obtained with six to seven times less of purealginate. Taking into account the relatively higher price of purealginate, the saving obtained is about three to five times with respectto the actual net cost, this saving being considerable in this fieldhaving regard to the large quantities of water treated.

The present invention, therefore, enables what is, in fact, the mosteffective quality of alginate to be used in water treatment, this highquality alginate having hitherto been avoided because of its apparentlack of effectiveness.

Iclaim:

1. In a method of clarifying water which comprises flocculatingimpurities therefrom with a flocculating agent, an improvementcomprising adding to the water to be clarified, a flocculation additivewhich is a dispersion consisting of l g. of cellulose-free sodiumalginate per liter of demineralized water titrating at less than 10hydrotimetric, said dispersion being added to the water to be clarifiedin an amount corresponding to a concentration of 0.2 to 0.5 p.p.m. ofsodium alginate.

